Some months ago it was easy toggling it on and off with the "Z" button but that doesn't seem the case anymore. I've tried many times using the Quest Journal menu but it always reappears and has me pretty annoyed.
If you started a new character since this summer, Z is no longer by default bound to that function. Regardless, it might be good to check your keybinds to verify that it is set correctly for you.
One workaround that might be of use would be to find a quest that has no path, manually set it as active and then never complete the quest. Not sure what would be best but something relating to a task in the campaign window would be optimal. I used to do this all the time in Oblivion years ago.
"We have always been at war with Dread Vault" ~ Little Brother
When this happens to me I think it may be a part of the graphics degradation problem that is going around for a lot of people. Usually I can still see the quest path in my mini-map in the upper right corner. The only thing that fixes it for me is completely exiting the game and re-launching.
Answers